This invention generally relates to intravascular catheters, such as balloon catheters used in percutaneous transluminal coronary angioplasty (PTCA).
PTCA is a widely used procedure for the treatment of coronary heart disease. In this procedure, a balloon catheter is advanced into the patient""s coronary artery and the balloon on the catheter is inflated within the stenotic region of the patient""s artery to open up the arterial passageway and thereby increase the blood flow there through. To facilitate the advancement of the catheter into the patient""s coronary artery, a guiding catheter having a preshaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by the Seldinger technique through the brachial or femoral arteries. The guiding catheter is advanced until the preshaped distal tip of the guiding catheter is disposed within the ascending aorta adjacent the ostium of the desired coronary artery, and the distal tip of the guiding catheter is then maneuvered into the ostium. A balloon catheter may then be advanced through the guiding catheter into the patient""s coronary artery over a guidewire until the balloon on the catheter is disposed within the stenotic region of the patient""s artery.
The balloon is inflated to open up the arterial passageway and increase the blood flow through the artery. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilation but not over expand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In a large number of angioplasty procedures, there may be a restenosis, i.e. reformation of the arterial plaque in the dilated arterial region. To reduce the restenosis rate and to strengthen the dilated area, physicians now frequently implant an intravascular prosthesis called a stent inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the expanded stent is left in place within the artery.
Radiopaque markers, typically in the form of bands of radiopaque material, are used to mark the working length of the balloon and help physicians to determine the location of the balloon inside a vessel. Radiopaque markers are typically placed on a distal section of the shaft inner tubular member which extends through the interior of the balloon. During assembly of the catheter, the balloon is moved into place over the inner tubular member and the radiopaque markers are visually lined up to correspond with the proximal and the distal ends of the working length of the balloon. Radiopaque markers can also be used to mark the proximal and the distal ends of a stent mounted on the balloon.
Catheter balloons formed of opaque materials such as expanded polytetrafluoroethylene (ePTFE) are not able to be adequately positioned relative to the radiopaque markers due to the inability to visualize the markers through the balloon. Placement of an opaque balloon may be done by referencing the location of the two markers on an outside fixture. However, using outside fixtures for referencing when placing a balloon is not a very accurate technique. Misplacement of the balloon with respect to the radiopaque marker bands may result in later errors in judgement of the balloon location within a patient. What has been needed is a method and a balloon to allow visualization of marker bands through an opaque balloon.
The present invention is directed to a method and medical device component allowing visualization through the opaque material used to form the component. In a method of the invention for visualization through a medical device; component formed of a porous opaque material, a fluid is applied to the porous material which has a refractive index substantially similar to the refractive index of the porous material, so that the transparency of the porous material is increased.
In a presently preferred embodiment the porous material is expanded polytetrafluoroethylene (ePTFE). The porous ePTFE is opaque due to its porous nature. Specifically, the refractive indexes of the ePTFE and air in the porous ePTFE are sufficiently different to cause the scattering of light waves, thus rendering the ePTFE opaque. In accordance with the invention, the material applied to the porous ePTFE fills the spaces of the ePTFE which would otherwise be filled with air, and has a refractive index substantially similar to that of the ePTFE, so that the ePTFE becomes sufficiently transparent to allow visualization therethrough. In a presently preferred embodiment, the substantially similar refractive index of the material in the pores of the porous material is within about 5% to about 20%, preferably within about 5% to about 10% of the refractive index of the porous material (i.e., the refractive index of the material in the pores is xc2x15% to xc2x120% of the refractive index of the porous material).
A variety of suitable materials having a refractive index substantially similar to that of the porous material may be used to increase the transparency of the porous material. In one embodiment, the material in the pores of the porous material is selected from the group consisting of alcohol and silicone. In a presently preferred embodiment, the alcohol is isopropyl alcohol, and the silicone is a silicone-based adhesive such as MED62-15, available from Nusil Technology. In one embodiment, the silicone-based adhesive has an elongation of about 100% to about 600%. A device containing the fluid, such as a pipette, can be used to place the fluid onto the balloon. However a variety of suitable methods can be used to apply the fluid to the porous material, including immersing at least a section, or spraying the fluid on at least a section, of the porous material.
In a presently preferred embodiment, the medical device component is a balloon for a catheter such as an angioplasty catheter or a stent delivery catheter. However, a variety of suitable medical device components formed of porous opaque material may be used including covers for stents or catheter balloons, grafts, and the like. A balloon of the invention formed of a porous opaque material having at least a section which is completely or partially transparent allows for visualization of radiopaque marker bands placed on the catheter shaft underneath the balloon, thereby facilitating assembly of the balloon catheter. Preferably, the transparent sections are at or adjacent to the ends of the working length of the balloon or centrally located along at least a section of the working length, to facilitate radiopaque marker visualization. However, transparent section(s) of the balloon can be provided at a variety of desired locations on the balloon, including extending the entire working length or the entire length of the balloon.
The medical device component of the invention is at least in part transparent due to the fluid applied to the otherwise opaque material forming the component. The increased transparency of the component such as a catheter balloon facilitates assembly of the catheter by allowing for visualization through the balloon of radiopaque markers on the catheter shaft. Additionally, the markers can be visualized during stent placement on the balloon and as a result would also be facilitated by the present invention because the stent could be accurately positioned with respect to the markers. These and other advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying exemplary drawings.